net: ethernet: mtk_eth_soc: fix PPE hanging issue

A patch to resolve an issue was found in MediaTek's GPL-licensed SDK:
In the mtk_ppe_stop() function, the PPE scan mode is not disabled before
disabling the PPE. This can potentially lead to a hang during the process
of disabling the PPE.

Without this patch, the PPE may experience a hang during the reboot test.

Link: https://git01.mediatek.com/plugins/gitiles/openwrt/feeds/mtk-openwrt-feeds/+/b40da332dfe763932a82f9f62a4709457a15dd6c
Fixes: ba37b7ca ("net: ethernet: mtk_eth_soc: add support for initializing the PPE")
Suggested-by: Bc-bocun Chen <bc-bocun.chen@mediatek.com>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mediatek/mtk_ppe.c

@@ -994,7 +994,7 @@ void mtk_ppe_start(struct mtk_ppe *ppe)
 			 MTK_PPE_KEEPALIVE_DISABLE) |
 	      FIELD_PREP(MTK_PPE_TB_CFG_HASH_MODE, 1) |
 	      FIELD_PREP(MTK_PPE_TB_CFG_SCAN_MODE,
-			 MTK_PPE_SCAN_MODE_KEEPALIVE_AGE) |
+			 MTK_PPE_SCAN_MODE_CHECK_AGE) |
 	      FIELD_PREP(MTK_PPE_TB_CFG_ENTRY_NUM,
 			 MTK_PPE_ENTRIES_SHIFT);
 	if (mtk_is_netsys_v2_or_greater(ppe->eth))
@@ -1090,17 +1090,21 @@ int mtk_ppe_stop(struct mtk_ppe *ppe)
 
 	mtk_ppe_cache_enable(ppe, false);
 
-	/* disable offload engine */
-	ppe_clear(ppe, MTK_PPE_GLO_CFG, MTK_PPE_GLO_CFG_EN);
-	ppe_w32(ppe, MTK_PPE_FLOW_CFG, 0);
-
 	/* disable aging */
 	val = MTK_PPE_TB_CFG_AGE_NON_L4 |
 	      MTK_PPE_TB_CFG_AGE_UNBIND |
 	      MTK_PPE_TB_CFG_AGE_TCP |
 	      MTK_PPE_TB_CFG_AGE_UDP |
-	      MTK_PPE_TB_CFG_AGE_TCP_FIN;
+	      MTK_PPE_TB_CFG_AGE_TCP_FIN |
+		  MTK_PPE_TB_CFG_SCAN_MODE;
 	ppe_clear(ppe, MTK_PPE_TB_CFG, val);
 
-	return mtk_ppe_wait_busy(ppe);
+	if (mtk_ppe_wait_busy(ppe))
+		return -ETIMEDOUT;
+
+	/* disable offload engine */
+	ppe_clear(ppe, MTK_PPE_GLO_CFG, MTK_PPE_GLO_CFG_EN);
+	ppe_w32(ppe, MTK_PPE_FLOW_CFG, 0);
+
+	return 0;
 }